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Expression of the nifH Gene of a Herbaspirillum Endophyte in Wild Rice Species: Daily Rhythm during the Light-Dark Cycle

By Mu You, Tomohiro Nishiguchi, Asami Saito, Tsuyoshi Isawa and Hisayuki Mitsui

Abstract

The expression of nitrogenase genes of Herbaspirillum sp. B501 associated in shoot (leaf and stem) of wild rice, Oryza officinalis, was studied by means of reverse transcription-PCR (RT-PCR) targeted at the nifH gene. RT-PCR analyses indicate that nifH transcript was detected exclusively from nitrogen-fixing cells of gfp-tagged strain B501gfp1 in both free-living and endophytic states by using a constitutive gfp gene transcript as a positive control. Transcription of nifH and nitrogen fixation in free-living cells were induced maximally at a 2 % O 2 concentration and repressed in free air (21 % O 2). nifH transcription was monitored in the endophytic cells by using total RNA extracted from B501gfp1-inoculated wild rice plants during daily light-dark cycles. The level of nifH transcription in planta varied dramatically, with a maximum during the light period. Moreover, the light radiation enhanced nifH expression even in free-living cells grown in culture. These results suggest that in planta nitrogen fixation by the endophyte shows a daily rhythm determined by the plant’s light environment. The availability of fixed nitrogen limits primary productivity in plant ecosystems (6). During their evolution, legumes have developed a symbiotic partnership with rhizobia that can fix atmospheric nitrogen and can thus attain the necessary fixed nitrogen. Among nonleguminous plants, several genera of diazotrophs have been isolated and characterized as nitrogenfixin

Year: 2005
OAI identifier: oai:CiteSeerX.psu:10.1.1.320.6736
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